1. Field of the Invention
This invention relates to a method of determining the contents in percentage of constituents in molten iron by measuring the emission spectrum produced at the surface thereof. The method according to this invention is applicable, for example, to the analysis of constituents of molten iron contained in a basic oxygen converter.
2. Description of the Prior Art
For proper control of such operations as metal refining and steelmaking processes, it is necessary to grasp the contents of constituents in the metal being processed through quick analysis and take necessary corrective measure, if needed, based on the obtained analytical data. To permit such an approach, various types of quick-analysis methods have been proposed and put to use for many analytical activities for process and quality control in steel and other metal industries.
For such analyses intended for the control of metal production processes, spark spectroscopy has been widely employed, in which solid block specimens prepared from sampled molten metal are used. But in recent years, the steel industry, for instance, has come to feel the need of achieving faster control techniques for conventional production processes and, at the same time, developing new controlling methods suited to many new production processes such as a steelmaking technique involving multistage refining. As such, there have been increasing need for the development of on-line real-time analysis techniques dealing directly with such molten metals as molten iron and steel.
With such purposes in mind, several spectroscopic techniques have been studied; some examples of which include a method that turns molten metal into fine powder using a special-purpose atomizer that uses argon gas and introduces the obtained powder to an emission spectrometer (BISRA Annual Report: 78(1966), 65, 78(1967), 35(1968)) and a method that identifies constituents of molten steel by optically detecting the absorption spectrum of constituents contained in gases released therefrom (Japanese Provisional Patent Publication No. 145336-1981). But these new techniques have been only tested on laboratory scale, not yet having been put to commercial use.
The inventors, too, have developed methods of spectroscopically analyzing fine particles containing representative constituents of molten metal that are vaporized by excitation through the passing of such electric discharge as plasma arc and spark or the irradiation of laser beams to molten metal (Japanese Patent Application Nos. 201154-1981 and 30879-1983) and methods of spectroscopically analyzing fine particles vaporized, and collected, from the surface of molten metal on the introduction of an inert gas from the top of a hermetically sealed vessel, at the bottom of which molten metal is captured (Japanese Patent Applications Nos. 16965-1984, 16966-1984, 16967-1984 and 75034-1984), with patent pending.
In the aforementioned methods, however, uniform clearance must be kept between the surface of molten metal and the tip of an excitation source such as a spark discharging electrode. Also, part of the apparatus must be immersed in molten metal. But molten meta, more often than not, is stirred or agitated, undergoes bath level fluctuations and flows in streams. Consequently, means to control or follow such variations should be provided. Where part of the apparatus (such as a probe) is brought in contact with or immersed in molten metal, the need of preventing the damage and erosion of the probe by the attack of the molten metal and protecting the probe from the chemical reaction between itself and the molten metal arises. In practice, however, violent changes in the metal bath level are hardly followed satisfactorily in the conventional spectroscopical methods employing spark and laser excitation. With the methods in which fine particles are collected by means of sampling probe immersed in molten metal, on the other hand, it has been difficult to keep the probe immersed in a stable condition without getting damaged where the molten metal is stirred or flows in streams.